It’s interesting that people think happy posts must equal unhappy person. And yet when people post sad things, they are also accused of being an attention seeker or drama llama. You can’t really win.
I think it's a case of knowing the people.
I know people who share loads of nice things. It would never occur to me that they were compensating for anything.
I also know people who share more gushy romantic things, selfies of them kissing, wishing each other a happy anniversary, thank you for being the best mummy/daddy, but I know they've not been in a good place.
Sharing sad things doesn't always make someone a drama llama. It's the difference between an update on something sad and "Louise has checked into Town Hospital A&E" / "I just want to share millions of things about mental health even though I've never got help, but it's my topic for the next month about how hard everything is for me, but next month I'll be posting about why most of us have fibromyalgia (revolving door of sympathy topics which makes a mockery of those with difficulties), or the relationship updates, or cryptic vague booking "I guess this week has shown me I can't trust most people. Time for wine!"
As another poster said, it's often what is/isn't shared gives away some clues.